1. Field of the Invention
This invention relates to integrated circuit structures. More particularly, this invention relates to a process for filling contact openings and vias in an insulating layer with the same metal used for forming a metal interconnect or wiring harness over the insulating layer.
2. Description of the Related Art
In the formation of integrated circuit structures, an insulating layer is formed over the active devices, or over a patterned underlying metal interconnect layer, and vertical openings are then formed through this insulating layer to provide electrical communication from the upper surface of the insulating layer to the underlying active device or electrical interconnect. Such openings are then filled with an electrically conductive material to provide electrical connection between the underlying elements and conductive materials, such as a metal interconnect or wiring harness, subsequently formed on the surface of the insulating material.
When an opening is formed through the first insulating layer down to the active device (or associated passive devices such as resistors) the opening through the insulating layer is usually referred to as a contact opening, while an opening through a subsequent insulating layer to an underlying metal interconnect is usually referred to as a via. For purposes of this invention, no distinction will be made between the terms "via" and "contact opening" and the terms will be used interchangeably herein.
Aluminum has been the metal or alloy of choice for use in the formation of patterned interconnects or "wiring" on the surface of insulating layers, due to its high conductivity, low cost, and compatibility with other materials used in the construction of the integrated circuit structure. In the past, when larger dimensions were used for line widths and contact opening diameters, contact openings or vias were formed in the insulating layer and a layer of aluminum was then formed over the insulating layer which also filled the contact openings as well, although barrier material, such as TiN was usually used when the aluminum would otherwise contact silicon, to avoid migration of Si or Al atoms into the other material.
However, as dimensions of lines and contact openings decreased, with ever increasing scale of VLSI structures, problems arose with securing satisfactory filling of the entire contact opening with the aluminum used to form the contact layer over the insulating layer. This, in turn, has given rise to the use of other filler materials such as tungsten to fill the contact opening prior to the formation of the aluminum layer over the insulating layer. After formation of, for example, a barrier layer of TiN, a layer of tungsten is deposited over the barrier layer and insulating layer which also fills the contact opening after which the structure is planarized to remove all of the surface tungsten (leaving only the tungsten in the contact openings). The aluminum layer is then formed over the insulating layer which aluminum layer thereby makes electrical contact with the upper exposed surface of the underlying tungsten in the contact opening.
While this approach has solved the problem of adequate filling of small contact openings with conductive material, the use of tungsten as a filler material results in other problems. Filling the openings with tungsten adds further deposition and planarization steps to the process, resulting in more complexity, more cost, and less reliability. In addition, the use of tungsten metal results in higher particle formation possibilities, higher resistivity of the tungsten compared to aluminum, and a metal interface wherein the crystallographic disposition of the tungsten can, in turn, affect the crystallographic form of the aluminum subsequently deposited therein, i.e., by the tungsten surface providing a seed surface for the aluminum deposition, thereby sometimes resulting in the subsequent formation of a less desirable crystallographic form of aluminum.
It would, therefore, be highly desirable to be able to fill very small diameter openings in an insulation layer with metal such aluminum initially deposited on the surface of the insulating layer and then later patterned to form a metal interconnect layer, i.e., to use the same metal to both fill the openings in the insulation layer and to form the electrically conductive interconnect or wiring harness on the surface of the insulating layer.